Magnetic recording medium comprising multilayered carbon-containing protective overcoats

ABSTRACT

A magnetic recording medium is provided with dual carbon-containing protective overcoats for high magnetic recording performance and high mechanical performance. Embodiments include a dual protective overcoat comprising an amorphous carbon layer on a magnetic layer and a nitrogenated carbon layer on the amorphous carbon layer.

RELATED APPLICATION

This application claims priority from provisional patent applicationSerial No. 60/082,181 filed Apr. 16, 1998, the entire disclosure ofwhich is hereby incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a magnetic recording medium,particularly a rotatable magnetic recording medium, such as a thin filmmagnetic disk cooperating with a magnetic transducer head. The inventionhas particular applicability to high areal recording density magneticrecording media designed for drive programs having reduced flyingheights, or pseudocontact/proximity recording.

BACKGROUND ART

Thin film magnetic recording disks and disk drives are conventionallyemployed for storing large amounts of data in magnetizable form. Inoperation, a typical contact start/stop (CSS) method commences when adata transducing head begins to slide against the surface of the disk asthe disk begins to rotate. Upon reaching a predetermined high rotationalspeed, the head floats in air at a predetermined distance from thesurface of the disk where it is maintained during reading and recordingoperations. Upon terminating operation of the disk drive, the head againbegins to slide against the surface of the disk and eventually stops incontact with and pressing against the disk. Each time the head and diskassembly is driven, the sliding surface of the head repeats the cyclicoperation consisting of stopping, sliding against the surface of thedisk, floating in the air, sliding against the surface of the disk andstopping.

For optimum consistency and predictability, it is necessary to maintaineach transducer head as close to its associated recording surface aspossible, i.e., to minimize the flying height of the head. Accordingly,a smooth recording surface is preferred, as well as a smooth opposingsurface of the associated transducer head. However, if the head surfaceand the recording surface are too flat, the precision match of thesesurfaces gives rise to excessive stiction and friction during the startup and stopping phases, thereby causing wear to the head and recordingsurfaces, eventually leading to what is referred to as a “head crash.”Thus, there are competing goals of reduced head/disk friction andminimum transducer flying height.

Conventional practices for addressing these apparently competingobjectives involve providing a magnetic disk with a roughened recordingsurface to reduce the head/disk friction by techniques generallyreferred to as “texturing.” Conventional texturing techniques involvemechanical polishing or laser texturing the surface of a disk substrateto provide a texture thereon prior to subsequent deposition of layers,such as an underlayer, a magnetic layer, a protective overcoat, and alubricant topcoat, wherein the textured surface on the substrate isintended to be substantially replicated in the subsequently depositedlayers. The surface of an underlayer can also be textured, and thetexture substantially replicated in subsequently deposited layers.

A typical longitudinal recording medium is depicted in FIG. 1 andcomprises a substrate 10, typically an aluminum (Al)-alloy, such as analuminum-magnesium (Al-Mg)-alloy, plated with a layer of amorphousnickelphosphorus (NiP). Alternative substrates include glass,glass-ceramic materials, plastics, silicon and graphite. Substrate 10typically contains sequentially deposited on each side thereof achromium (Cr) or Cr-alloy underlayer 11, 11′, a cobalt (Co)-base alloymagnetic layer 12, 12′, a protective overcoat 13, 13′, typicallycontaining carbon, and a lubricant topcoat 14, 14′. Cr underlayer 11,11′ can be applied as a composite comprising a plurality ofsub-underlayers 11A, 11A′. Cr underlayer 11, 11′, Co-base alloy magneticlayer 12, 12′ and protective overcoat 13, 13′, typically containingcarbon, are usually deposited by sputtering techniques performed in anapparatus containing sequential deposition chambers. A conventionalAl-alloy substrate is provided with a NiP plating, primarily to increasethe hardness of the Al substrate, serving as a suitable surface toprovide a texture, which is substantially reproduced on the disksurface.

In accordance with conventional practices, a lubricant topcoat isuniformly applied over the protective overcoat to prevent wear betweenthe disk and head interface during drive operation. Excessive wear ofthe protective overcoat increases friction between the head and disk,thereby causing catastrophic drive failure. Excess lubricant at thehead-disk interface causes high stiction between the head and disk. Ifstiction is excessive, the drive cannot start and catastrophic failureoccurs. Accordingly, the lubricant thickness must be optimized forstiction and friction.

A conventional material employed for the lubricant topcoat comprises aperfluoro polyether (PFPE) which consists essentially of carbon,fluorine and oxygen atoms. The lubricant is usually dissolved in anorganic solvent applied and bonded to the carbon overcoat of themagnetic recording medium by techniques such as thermal treatment,ultraviolet (UV) irradiation and soaking. A significant factor in theperformance of a lubricant topcoat is the bonded lube ratio which is theratio of the amount of lubricant bonded directly to the carbon overcoatof the magnetic recording medium to the amount of lubricant bonded toitself or to a mobile lubricant. Desirably, the bonded lube ratio shouldbe high to realize a meaningful improvement in stiction and wearperformance of the resulting magnetic recording medium.

The escalating requirements for high areal recording density imposeincreasingly greater requirements on thin film magnetic media in termsof coercivity, stiction, squareness, low medium noise and narrow trackrecording performance. In addition, increasingly high areal recordingdensity and large-capacity magnetic disks require increasingly smallerflying heights, i.e., the distance by which the head floats above thesurface of the disk in the CSS drive (head-disk interface). Forconventional media design, a decrease in the head to media spacingincreases stiction and drive crash, thereby imposing an indispensablerole on the carbon-protective overcoat.

There are various types of carbon, some of which have been employed fora protective overcoat in manufacturing a magnetic recording medium. Suchtypes of carbon include hydrogenated carbon, graphitic carbon orgraphite and nitrogenated carbon or carbon nitride. These types ofcarbon are well known in the art and, hence, not set forth herein ingreat detail. See, for example, L. J. Huang et al., “Structure ofNitrogenated Carbon Overcoats on Thin Film Hard Disks,” IEEE Transactionon Magnetics, Vol. 33, 1997; L. J. Huang et al., “Characterization ofthe head-disk interface for proximity recording,” IEEE Transaction onMagnetics, 1997, Vol. 33, pp. 3112-3114; and Tsai et al., “CharacterReview Characterization of diamond like carbon films and theirapplication as overcoats on thin-film media for magnetic recording,” J.Vac. Sci. Technol., A5(6), Nov/Dec, 1987, pp. 3287-3311.

Generally, hydrogenated carbon has a hydrogen concentration of about 5at. % to about 40 at. %, typically about 20 at. % to about 30 at. %, anddoes not bond well to a subsequently applied lubricant topcoat by virtueof the passivation of carbon dangling bonds by hydrogen. Accordingly, itis difficult to effectively bond a lubricant topcoat to a hydrogenatedcarbon protective overcoat at a suitable thickness. Hydrogenated carbonhas a lower conductivity due to the elimination of the carbon band-gapstates by hydrogen. Hydrogenated carbon also provides effectivecorrosion protection to an underlying magnetic layer.

Amorphous carbon nitride, sometimes referred to as nitrogenated carbon,generally has a nitrogen to hydrogen concentration ratio of about 5:20to about 30:0. Carbon nitride generally has more carbon band-gap statesthan hydrogenated carbon and, hence, a higher conductivity. In addition,carbon nitride contains more dangling bonds than hydrogenated carbon,which dangling bonds promote interactions between lubricant and carbonand, hence, enable the application of a thicker bonded lubricanttopcoat. Graphitic carbon or graphite contains substantially no hydrogenand nitrogen and has less band-gap states vis-à-vis nitrogenated carbonbut more band-gap states than hydrogenated carbon.

The drive for high areal recording density and, consequently, reducedflying heights, challenges the limitations of conventional practices inmanufacturing a magnetic recording medium containing a carbon protectiveovercoat. For example, a suitable protective overcoat must be capable ofpreventing corrosion of the underlying magnetic layer, which is anelectrochemical phenomenon dependent upon factors such as environmentalconditions, e.g., humidity and temperature. In addition, a suitableprotective overcoat must prevent migration of ions from underlyinglayers into the lubricant topcoat and to the surface of the magneticrecording medium forming defects such as asperities. A protectiveovercoat must also exhibit the requisite surface polarity to enablebonding thereto of a lubricant topcoat in an adequate thickness. Aprotective overcoat must also exhibit a suitable electricalconductivity. The absence of conductivity may result in the formation ofa static charge on the surface of the magnetic recording medium leadingto recording and/or reading errors. Furthermore, as the head diskinterface decreases to less than 1 microinch, it is necessary to reducethe thickness of the carboncontaining protective overcoat to below theconventional thicknesses employed, e.g., about 200 Å. It is virtuallyimpossible to satisfy such imposing requirements with a conventionalprotective overcoat material.

Accordingly, there exists a need for a magnetic recording mediumcomprising a protective overcoat capable of satisfying the imposingdemands for high areal recording density and reduced head diskinterface. There also exists a need for a magnetic recording mediumhaving a protective overcoat capable of preventing corrosion of theunderlying magnetic layer, preventing migration of ions from underlyinglayers, providing a suitable surface polarity for adequate lubricantbonding and exhibiting suitable conductivity to avoid reading and/orrecording errors. There exists a particular need for such a magneticrecording medium exhibiting improved magnetic recording performance,e.g., high remnant coercivity (Hr) and a high signal to noise ratio(SNR).

DISCLOSURE OF THE INVENTION

An object of the present invention is a magnetic recording mediumexhibiting high recording performance, a high SNR , and a high arearecording density.

Another object of the present invention is a magnetic recording mediumcomprising a thin protective overcoat capable of preventing corrosion ofthe underlying magnetic layer, migration of ions from underlying layers,or migration of atoms or ions from the overcoat to the magnetic layer orunderlayers, exhibiting a suitable surface polarity for lubricantbonding and a suitable conductivity.

A further object of the present invention is a method of manufacturing ahigh areal recording density magnetic recording medium exhibiting highrecording performance, a high SNR and suitable for use in a drive systemwith a flying height less than about 1.1 microinch.

Additional objects, advantages and other features of the presentinvention will be set forth in part in the description which follows andin part will become apparent to those having ordinary skill in the artupon examination of the following disclosure or may be learned from thepractice of the present invention. The objects and advantages of thepresent invention may be realized and obtained as particularly pointedout in the appended claims.

According to the present invention, the foregoing and other objects areachieved in part by a magnetic recording medium comprising an amorphouscarbon overcoat and a nitrogenated carbon overcoat deposited thereon.

Another aspect of the present invention is a method of manufacturing amagnetic recording medium, the method comprising depositing an amorphouscarbon protective overcoat on a magnetic layer and depositing anitrogenated carbon overcoat on the amorphous carbon protectiveovercoat.

Additional objects and advantages of the present invention will becomereadily apparent to those having ordinary skill in the art from thefollowing detailed description, wherein the embodiments of the presentinvention are described, simply by way of illustration of the best modecontemplated for carrying out the present invention. As will berealized, the present invention is capable of other and differentembodiments, and its several details are capable of modifications invarious obvious respects, all without departing from the presentinvention. Accordingly, the drawings and description are to be regardedas illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates a conventional magnetic recordingmedium.

FIG. 2 schematically illustrates a magnetic recording medium inaccordance with an embodiment of the present invention.

FIGS. 3A and 3B illustrate the Hr and SNR, respectively, of anembodiment of the present invention vis-à-vis a conventional magneticrecording medium.

DESCRIPTION OF THE INVENTION

The present invention enables the manufacture of magnetic recordingmedia exhibiting improved magnetic recording and mechanical performancesuitable for high area recording density in a cost effective, efficientmanner. Embodiments of the present invention comprise forming acomposite protective overcoat comprising a plurality ofcarbon-containing layers with an attendant increase in Hr and SNR and anarrower signal pulse. The composite protective overcoat of the presentinvention further prevents corrosion of the underlying magnetic layer,prevents migration of ions from underlying layers, or migration of atomsor ions from the overcoat to the magnetic layer or underlayer, causing adeterioration of recording performance, enables adequate bonding of alubricant topcoat thereto at a desirable thickness, such as about 5 Å toabout 10 Å, and exhibits a suitable conductivity to avoid reading and/orwriting errors.

Embodiments of the present invention include forming a dualcarbon-containing protective overcoat comprises a first relatively thinlayer of amorphous carbon deposited on a magnetic layer and a secondrelatively thick layer of nitrogenated carbon deposited on the firstamorphous carbon layer thereon. The first carbon layer is typicallysputter deposited on a magnetic layer comprising a magnetic materialconventionally employed in the manufacture of magnetic recording media,such as a Co alloy, e.g., a cobalt-chromium-platinum alloy, acobalt-chromium-tantalum alloy or a cobalt-chromium-platinum-tantalumalloy. Magnetic recording media according to the present invention cancomprise a single, double or multi-underlayer structure. The underlayerstructure is typically sputter deposited on a conventional non-magneticsubstrate, such as an Al aluminum alloy substrate or an alternatesubstrate such as a glass, ceramic or a glass-ceramic substrate. Thecarbon-containing protective overcoats can be deposited by sputterdepositing in a DC magnetron sputtering apparatus employing a basepressure of about 10⁻⁷Torr. The substrate can be heated to in excess of100° C. employing a sputtering pressure of about 5 to about 15 mTorr.

In an embodiment of the present invention, a magnetic recording mediumis formed with a first layer of amorphous carbon, typically at athickness of about 1 Å to about 200 Å. A second protective layercomprising nitrogenated carbon is then sputter deposited on the firstamorphous carbon layer at a thickness of about 1 Å to about 500 Å. Theamorphous carbon protective overcoat layer deposited in accordance withembodiments of the present invention is characterized by degenerate orimperfect graphitic structures and is substantially free of nitrogen,e.g., less than about 5 wt. % nitrogen.

An embodiment of the present invention is illustrated in FIG. 2, whereinelements similar to those of the conventional magnetic recordingillustrated in FIG. 1 bear similar reference numerals. As shown in FIG.2, substrate 10 is provided sequentially, on each side thereof, with aCr or Cr-alloy underlayer 11, 11′, and a magnetic layer, such as aCo-base alloy layer 12, 12′ thereon, as in the FIG. 1 magnetic recordingmedium. However, the magnetic recording medium in accordance with thepresent invention departs from the conventional magnetic recordingmedium illustrated in FIG. 1 in that the protective overcoat comprises aplurality of layers 20A, 20B and 20A′, 20B′, sequentially formed onmagnetic layer 12, 12′. First protective overcoat layer 20A, 20A′comprises amorphous carbon which is substantially free of nitrogen,while second protective overcoat layer 20A, 20B′ comprises nitrogenatedcarbon. A lubricant topcoat 14, 14′ is then applied to the secondcarbon-containing protective overcoat layer 20B, 20B′.

EXAMPLES Example 1

Two magnetic recording media were prepared employing substantially thesame components for the layers which were deposited under substantiallythe same deposition conditions, except for the protective overcoats.Each magnetic recording medium comprised a NiP plated Al substrate,NiAl/CrV dual underlayer and a magnetic layer comprising CoCrPtTa. Onemedium (1A) represents a conventional magnetic recording mediumcontaining a single amorphous nitrogenated carbon protective overcoatdeposited on the magnetic layer at a thickness of about 100 Å. Thesecond medium (1B) represents an embodiment of the present inventioncontaining dual carbon-containing layers comprising a first amorphouscarbon layer deposited on the magnetic layer at a thickness of about 30Å and a nitrogenated carbon layer deposited thereon at a thickness ofabout 70 Å. The amorphous carbon layer was sputtered deposited in argon,while the nitrogenated carbon layers were deposited in a mixture ofargon and nitrogen gas.

Example 2

Two magnetic recording media were prepared, one conventional (2A) andone representative of the present invention (2B), as in Example 1,except that the magnetic layer comprised CoCrPtTaNb.

Example 3

Two magnetic recording media were prepared, one conventional (3A) andone representative of the present invention (3B), as in Example 1,except that the underlayer comprised a single CrV.

The magnetic properties of the media of Examples 1A-3A and 1B-3B weretested on a non-destructive rotating disk magnetometer. The recordingsignal and media were measured at 240 kfci(kiloflux reversal per inch)linear density employing a Guzik tester with a MR (magnetoresistive)head having a gap length of 0.5 μm flying at a height of 1.1 μinch. Theresults are reported in FIGS. 3A and 3B comparing the Hr and SNR for themedia comprising the single amorphous nitrogenated carbon overcoat withthe dual layer overcoat comprising an amorphous carbon layer and anitrogenated carbon layer deposited thereon.

It is apparent from FIGS. 3A and 3B that the dual carbon overcoat filmstructure in accordance with the present invention provides magneticrecording media exhibiting a significantly higher Hr which results in ashorter data bit length and magnetic transmission length, as well assignificantly lower media noise and narrower signal pulse, therebyensuring quality reading/writing and higher storage density ability. Thecomposite protective overcoat of the present invention also preventscorrosion of the underlying magnetic layer and migration of ions fromunderlying layers, or the migration of atoms or ions from the carbonovercoat to the magnetic layer which induces deterioration of recordingor magnetic performance, and enables suitable lubricant bonding thereto.

The mechanism involved in achieving the superior magnetic recording andwriting performance as well as high SNR due by employing a compositecarbon-containing overcoat in accordance with the embodiments of thepresent invention is not known with certainty. However, it is believedthat strategic positioning of an amorphous carbon protective overcoatsubstantially free of nitrogen between the magnetic layer and thenitrogenated carbon overcoat prevents nitrogen diffusion into themagnetic layer, thereby avoiding the formation of a FCC (face centeredcubic) phase which exhibits weak magnetocrystalline anisotropy and,hence, lower coercivity. Accordingly, the use of an amorphous carbonprotective overcoat containing substantially no nitrogen is believed topreserve the hcp (hexagonal close packed) interface of the magneticalloy layer.

The magnetic layer employed in the present invention as well as theunderlayer structure can be any of those conventionally employed in themanufacture of magnetic recording media. The magnetic alloy layer cancomprise any conventional Co alloy layer, such ascobalt-chromium-platinum, cobalt-chromium-tantalum,cobalt-chromium-platinum-tantalum orcobalt-chromium-platium-tantalum-niobium.

The present invention can be employed to produce any of various types ofmagnetic recording media, including thin film disks. The presentinvention is particularly applicable in producing high areal recordingdensity magnetic recording media requiring a low flying height.

Only the preferred embodiment of the present invention and but a fewexamples of its versatility are shown and described in the presentdisclosure. It is to be understood that the present invention is capableof use in various other combinations and environments and is capable ofchanges or modifications within the scope of the inventive concept asexpressed herein.

What is claimed is:
 1. A magnetic recording medium having a multilayered protective overcoat with a thickness less than about 100 Å andconsisting essentially of an amorphous carbon overcoat withsubstantially no diamond bonds and a nitrogenated carbon overcoatdeposited thereon.
 2. The magnetic recording medium according to claim1, wherein: the amorphous carbon overcoat has a thickness of about 1 Åto about 30 Å; the nitrogenated carbo n overcoat has a thickness ofabout 1 Å to about 70 Å, which is greater than the thickness of theamorphous carbon overcoat.
 3. The magnetic recording medium according toclaim 2, wherein the amorphous carbon overcoat has a thickness less thanabout 50% of the thickness of the nitrogenated carbon overcoat.
 4. Themagnetic recording medium according to claim 3, wherein the amorphouscarbon overcoat has a thickness of about 5 to less than 50% of thethickness of the nitrogenated carbon overcoat.
 5. The magnetic recordingmedium according to claim 1, wherein the amorphous carbon overcoat isformed on a magnetic layer having a predominant hexagonal close packedcrystal structure.
 6. The magnetic recording medium according to claim5, wherein: the magnetic layer comprises a cobalt alloy.
 7. The magneticrecording medium according to claim 6, wherein the magnetic alloycomprises a cobalt-chromium-platinum alloy, a cobalt-chromium-tantalumalloy, a cobalt-chromium-platinum-tantalum alloy, or acobalt-chromium-platinum-tantalum-niobium alloy.
 8. The magneticrecording medium according to claim 5, wherein the magnetic layer isformed on an underlayer which comprises either a single layer or amultilayer structure.
 9. The magnetic recording medium according toclaim 5, comprising: a non-magnetic substrate; at least one underlayeron the non-magnetic substrate; and the magnetic layer on the underlayer.10. The magnetic recording medium according to claim 1, wherein theamorphous layer contains substantially no nitrogen.
 11. A method ofmanufacturing a magnetic recording medium, the method comprising:depositing an overcoat consisting essentially of amorphous carbon withsubstantially no diamond bonds on a magnetic layer; and depositing anitrogenated carbon overcoat on the amorphous carbon protectiveovercoat, wherein the combined thickness of the amorphous carbonovercoat and the nitrogenated carbon overcoat is less than about 100 Å.12. The method according to claim 11, comprising: sputter depositing theamorphous carbon overcoat in a gaseous atmosphere comprising argon orargon and hydrogen; and sputter depositing the nitrogenated carbonovercoat in an atmosphere comprising argon and nitrogen.
 13. The methodaccording to claim 12, comprising: sputter depositing the amorphouscarbon overcoat in a gaseous atmosphere comprising argon and about 1 toabout 50 volume percent hydrogen; and sputter depositing thenitrogenated carbon protective overcoat in a gaseous atmospherecomprising nitrogen and argon, with the nitrogen volume ranging fromabout 5% to about 50%.
 14. The method according to claim 11, wherein theamorphous carbon overcoat contains substantially no nitrogen.
 15. Themethod according to claim 11, wherein: the amorphous carbon overcoat hasa thickness of about 1 Å to about 30 Å; and the nitrogenated carbonovercoat has a thickness of about 1 Å to about 70 Å.